Phthalocyanine compounds are useful as coatings, printing inks, catalysts or electronic materials. In recent years, they have been extensively studied particularly for their use as electrophotographic photoreceptor materials, optical recording materials and photoelectric conversion materials.
In general, phthalocyanine compounds are known to have several different crystal forms depending on the process of production or the process of treatment. The difference in crystal form is known to have a great influence on their photoelectric conversion characteristics. For example, known crystal forms of copper phthalocyanine compounds include .alpha.-, .pi.-, .chi.-, .rho.-, .gamma.- and .delta.-forms as well as a stable .beta.-form. It is known that these crystal forms are capable of mutual transformation by a mechanical strain, a sulfuric acid treatment, an organic solvent treatment, a heat treatment and the like as described, e.g., in U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989. Further, a relationship between the crystal form of copper phthalocyanine and electrophotographic sensitivity is described in JP-A-50-38543 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
With respect to titanyl phthalocyanine, various crystal forms in relation to electrophotographic characteristics have been reported. For example, JP-A-62-67094 describes a stable .beta.-form, JP-A-61-217050 describes an .alpha.-form obtained by acid pasting or solvent treatment. Other crystal forms are disclosed in JP-A-63-366, JP-A-63-20365, JP-A-64-17066, and JP-A-1-153757.
However, any of the above-described titanyl phthalocyanine compounds proposed to date has poor crystal form stability against solvents and therefore, when dispersed and coated, cannot hold its crystal form for a long period of time.
Moreover, it is still unsatisfactory in photosensitivity and durability when used as a photosensitive material. That is, electrophotographic characteristics of titanyl phthalocyanine crystals are liable to variation depending on the diameter of primary particles, the specific surface area or shape of crystal grains, the absorbed water content, etc., thus making it difficult to obtain an electrophotographic photoreceptor having stable performance properties.